The present invention relates to a scroll type compressor.
In the scroll type compressor, Japanese Unexamined Patent Publication No. 7-158570 discloses to prevent power loss, vibration and noise that are caused by an excessive compression of the scroll type compressor. In the Publication, a plurality of intermediate compression chambers, in which gas compression is in progress, is connected to a discharge port respectively through communication passages. In each communication passage, a relief valve is placed and is opened when the pressure in the intermediate compression chambers is higher than the pressure in the discharge port. Therefore, when the pressure in the discharge port is relatively low, the relief valve opens the communication passage and thus the intermediate compression chambers are directly connected to the discharge port. Thereby, the excessive compression of the scroll type compressor, in which gas compression continues until the compression chambers substantially reach the center of a scroll of a fixed spiral wall, is prevented.
In the above-mentioned Publication, however, a plurality of relief valves is placed so as to correspond to the intermediate compression chambers, respectively. This structure increases the number of parts of the scroll type compressor. Furthermore, a plurality of the relief valves generates pressure pulsation due to a time lag where each relief valve is opened. Thereby, abnormal sound and vibration generate.
The present invention is directed to a scroll type compressor which prevents an excessive compression by using a relatively small number of parts.
The present invention has a following feature. A scroll type compressor includes a housing, a movable scroll member, a plurality of compression chambers, a discharge port, a communication passage and a relief valve. The housing has a fixed scroll member which has a fixed base plate and a fixed spiral wall that extends from the fixed base plate. The movable scroll member is placed in the housing. The movable scroll member has a movable base plate and a movable spiral wall that extends from the movable base plate. The movable spiral wall is engaged with the fixed spiral wall. The compression chambers are defined between the movable scroll member and the fixed scroll member, and are moved radially and inwardly to compress gas by orbiting the movable scroll member relative to the fixed scroll member while reducing their volume. The compression chambers have at least a first intermediate compression chamber and a second intermediate compression chamber, in which gas compression is in progress, respectively. The discharge port is formed substantially at the center of the fixed base plate or the movable base plate for sending the compressed gas to an outside of the housing. The communication passage interconnects each intermediate compression chamber with the discharge port. The communication passage has at least a first portion and a second portion. The first portion extends from the first intermediate compression chamber and the second portion extends from the second intermediate compression chamber. The first portion and the second portion meet at a meeting point on the way in the communication passage before reaching the discharge port. The relief valve is placed between the meeting point and the discharge port inclusive of the meeting point in the communication passage. The relief valve opens the communication passage when the pressure in the first and the second intermediate pressure chambers is higher than the pressure in the discharge port.